This invention relates to a control device for a vehicle mounted a.c. generator, and particularly to such a device by which a peak value of a phase voltage of an armature winding of the generator is regulated when the generator is inoperative.
FIG. 1 is a circuit diagram of a conventional control device of this type, in which a generator 1 driven by an engine of the vehicle includes an armature winding 101 and a field winding 102. The letter P depicts an output terminal of one of the three phases of the armature winding 101, from which a phase voltage produced in the phase is derived. A rectifier 2 functions to fullwave-rectify the a.c. output voltage of the generator 1 and has output terminals 201, 202, and 203. The main output of the generator is derived from terminal 201. The voltage at terminal 202 is used to energize the field winding 102, and is applied to a voltage regulator 3. Terminal 203 is grounded.
The voltage regulator 3 serves to regulate the output voltage of the generator 1 to a predetermined value, and includes a voltage divider composed of a pair of series connected resistors 301 and 302 connected between terminal 202 and ground. The junction between the resistors 301 and 302 is connected through a Zener diode 303 to the base of a transistor 304.
The Zener diode 303 is turned on when the output voltage at terminal 202 exceeds a predetermined value set by the resistors 301 and 302 and by the Zender diode 303, and is turned off when the output voltage of the generator falls below the predetermined value.
The transistor 304 is turned on when the Zener diode 303 is turned on, and vice versa. A transistor 308 is connected in parallel to the transistor 304, and the emitters of these transistors are grounded. Their collectors are connected to the base of an output transistor 305.
The base of transistor 305 and a collector thereof are connected through a base resistor 306 and a diode 307 to the output terminal 202, respectively. The collector of transistor 305 is further connected through the field winding 102 to the output terminal 202. That is, the diode 307 is connected in parallel to the field winding 102 to absorb surges produced due to the on-off operation of the field winding.
An electrical load 5 of the vehicle is connected in parallel to a battery 4. The negative terminal of the battery is grounded and its positive terminal is connected to the output terminal 201.
The positive terminal of the battery 4 is connected through a series circuit including a key switch 6, an initial energizing resistor 7 and a reverse current blocking diode 8 to the output terminal 202.
An acceleration detector 9 is supplied with the phase voltage at point P of the armature winding 101 of the generator 1 to detect the rotational speed of the generator. The acceleration detector 9 is further supplied with signals from various sensors mounted on the vehicle to detect whether or not the vehicle is being accelerated. When the vehicle is being accelerated, the acceleration detector 9 produces an acceleration signal corresponding to the rotational speed of the generator and supplies it to other control devices of the vehicle.
The acceleration detector 9 comprises a transistor 901 which is normally in an on state, and is turned off when the vehicle is accelerated. The output of the acceleration detector 9 is supplied to the voltage regulator 3. The transistor 901 has a collector connected to the base of transistor 308 and, through a resistor 309, to the output terminal 202.
FIG. 2 shows a waveform of the phase voltage at point P of the generator 1 under control of the conventional control device.
In operation, when the key switch 6 is closed to start the engine, an initial energizing current is supplied from the battery 4 through the switch 6, the resistor 7 and the diode 8 to the field winding 102 of the generator 1 to enable the latter to operate. When the engine starts, the generator 1 commences its operation. The voltage regulator 3 is supplied with a voltage generated by the generator 1 from the output terminal 202 of the rectifier 2 and, when the supplied voltage exceeds a predetermined voltage, the Zener diode 303 and the output transistor 305 are turned on and off, respectively, to thereby cut off the field winding 102. On the other hand, when the supplied voltage is below the predetermined value, the Zener diode 303 and the transistor 305 are turned off and on, respectively, to allow a field current to flow through the field winding 102.
By repeating these operations, the output voltage of the generator 1 is regulated to the predetermined level by the voltage regulator 3.
The acceleration detector 9 is supplied with the phase voltage at terminal P of the generator in the form of a pulse train, a peak value of which is substantially equal to the predetermined level set by the voltage regulator 3 and a frequency of which corresponds to the rotational speed of the generator, as shown in region I in FIG. 2. When an acceleration of the vehicle is detected on the basis of the input signal from the sensors of the vehicle, the acceleration detector 9 provides an acceleration signal corresponding to the number of revolutions of the generator, which is supplied to the other control devices of the vehicle and upon which the transistor 901 is turned off to turn on the transistor 308 of the voltage regulator 3, so that the output transistor 305 is turned off regardless of the operation of the Zener diode 303, to cut off the current to the field winding 102 and thereby stop the power generation of the generator.
As described, when the acceleration detector 9 detects the acceleration of the vehicle, the generator 1 stops generating power and the drive torque required to drive the generator is removed from the mechanical load of the engine. Therefore, the acceleration performance of the engine is improved.
In such a conventional control device, however, when the generator ceases operation upon the detection of vehicle acceleration, the peak value of the phase voltage at point P is gradually lowered as shown in region II in FIG. 2 and, when the value becomes very small, the acceleration detector 9 can no longer supply an appropriate control signal to the vehicle control device.